Rotary index table assembly

ABSTRACT

A rotary index table assembly including an annular positioning mechanism (22) that cooperates with a lift mechanism (140) to accurately position a rotary index table (14) on a base (12). The annular positioning mechanism (22) includes a base mounted crown gear (24), a table mounted crown gear (26) and a movable crown gear (28) that is moved out of engagement with the base and table mounted crown gears to permit the indexing rotation and that is thereafter moved into engagement with the base and table mounted crown gears to locate the table with respect to the base while the lift mechanism (140) supports the table on the base by the movement of the movable crown gear (28) to permit the accurate positioning.

TECHNICAL FIELD

This invention relates to a rotary index table assembly for moving workpieces being processed.

BACKGROUND ART

Rotary index table assemblies for processing workpieces such as disclosed by U.S. Pat. No. 3,718,055 Maier have previously included three annular crown gears, with one annular crown gear mounted on a base of the assembly, with a second annular crown gear mounted on a rotary table of the assembly, and with the third annular crown gear movable into and out of engagement with the base and table mounted crown gears so as to selectively position the rotary table both circumferentially and radially with respect to the rotational axis. This circumferential and radial positioning about the rotational axis results from the fact that the teeth of the crown gears extend radially from the rotational axis and taper inwardly to thereby provide both modes of the positioning. Other rotary index table assemblies which utilize crown gears for positioning are disclosed by U.S. Pat. Nos. 3,889,555 Frank et al and 4,353,271 Pieczulewski. Also, U.S. Pat. No. 5,450,771 Carter et al discloses a rotary index table assembly wherein an air bearing is utilized to remove weight from a table during a rotary index movement prior to positioning by base and table mounted crown gears in association with a movable crown gear.

Driving rotation of rotary index tables has previously been accomplished by the use of worm gear sets. For example, U.S. Pat. Nos. 3,941,014 Benjamin et al and 4,159,658 Parkinson disclose straight worm gear sets that rotatively drive associated rotary tables during index in association with crown gears that provide positioning after the rotation. Furthermore, machine table movement has previously been provided by double enveloping worm gear sets such as disclosed by U.S. Pat. No. 3,824,892 Bondie et al and, as disclosed by U.S. Pat. No. 4,653,739 Moore, has been utilized to provide rotary positioning of a workpiece table. Such double enveloping worm gear sets have surface-to-surface contact as opposed to line contact provided by straight worm gear sets and thus have greater capacity to provide rotational driving of greater loads for the same size unit. Rotational positioning for indexing has also been previously provided by polygonal type drive couplings such as disclosed by U.S. Pat. No. 3,507,169 Signer wherein a rotary drive member having polygon surfaces distributes the driving force.

U.S. Pat. No. 4,380,939 discloses a rotary indexing table which includes wedging rings for providing clamping to prevent table rotation and which is unclamped to allow the indexing rotation. During the rotation, pressurized air is supplied to an annular chamber to lift the table for easier rotation.

DISCLOSURE OF INVENTION

An object of the present invention is to provide an improved rotary index table assembly.

In carrying out the above and other objects of the invention, the rotary index table assembly of the invention includes a base and a rotary index table having a central rotational axis and an outer periphery. A rotary drive of the assembly rotates the index table on the base for indexing rotation about the rotational axis. Stationary supports support the periphery of the table to prevent movement thereof during machining of a workpiece supported by the table. An annular positioning mechanism of the assembly includes a base mounted crown gear, a table mounted crown gear and a movable crown gear that is moved to disengage from the base mounted crown gear and the table mounted crown gear to permit the indexing rotation of the table and that is thereafter moved into engagement with the base mounted crown gear and the table mounted crown gear to locate the table with respect to the base after each indexing rotation. A lift mechanism of the table assembly removes weight of the table from the stationary supports by the impetus of the movable crown gear upon moving out of engagement with the base mounted crown gear and the table mounted crown gear to facilitate accurate table positioning when the movable crown gear is subsequently again moved into engagement with the base mounted crown gear and the table mounted crown gear after the indexing rotation of the table.

The lift mechanism of the table assembly includes lift members that are movable upwardly by the movable crown gear upon disengagement thereof from the base mounted crown gear and the table mounted crown gear to remove weight of the table from the stationary supports. The base of the table assembly includes an annular ring having vertical openings that receive the lift members, and the lift members extend vertically between the movable crown gear and the table after disengagement of the movable crown gear from the base and table mounted crown gears. Each lift member has a lower surface for engaging the movable crown gear and an upper surface for engaging the table.

In the preferred construction, each lift member includes at least one lift button providing the lower surface thereof for engaging the movable crown gear. Each lift member has a horizontally elongated shape having opposite ends. A pair of lift buttons are respectively mounted by the opposite ends of each lift member and cooperatively provide the lower surface thereof for engaging the movable crown gear. Each lift member also preferably includes a third lift button mounted between the pair of lift buttons at the opposite ends thereof and cooperating therewith to provide the lower surface thereof for engaging the movable crown gear.

In the preferred construction, the table of the table assembly has a lower glide ring of an annular shape that is engaged by the upper surfaces of the lift members. A lubrication system of the lift mechanism provides lubrication between the lower guide ring of the table and the lift members. This lubrication system includes lubrication wicks mounted by the annular ring of the base between the vertical openings that receive the lift members. The lubrication system also includes lubrication passages for feeding a lubrication fluid to the wicks to provide lubrication between the upper surfaces of the lift members and the lower glide ring of the table.

The preferred construction of each lift member also includes at least one elastomeric locator for restraining movement thereof within the associated vertical opening of the annular ring of the base. Each lift member has a horizontally elongated shape and a pair of the elastomeric locators as well as having a pair of horizontal holes extending therethrough with the pair of elastomeric locators respectively extending through the pair of horizontal holes and having opposite ends that engage the annular ring of the base within the associated vertical opening thereof to restrain the lift member movement.

In its preferred construction, the rotary index table assembly has the annular positioning mechanism provided with a plurality of springs that bias the movable crown gear into engagement with the base mounted crown gear and the table mounted crown gear. The movable crown gear includes an annular piston portion, and the positioning mechanism also includes a hydraulic circuit that selectively provides pressurized hydraulic fluid to the piston portion of the movable crown gear to thereby provide movement thereof against the bias of the springs out of engagement with the base mounted crown gear and the table mounted crown gear to permit the indexing rotation under the impetus of the rotary drive.

In the preferred construction of the rotary index table assembly, the piston portion of the movable crown gear extends inwardly toward the rotational axis. In addition, the springs that bias the movable crown gear are located outwardly from the piston portion thereof in alignment with both the base mounted crown gear and the table mounted crown gear.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1a and 1b are respectively partial left and right elevational views taken in section through a rotary index table assembly constructed in accordance with the present invention and cooperatively when placed in a slightly overlapping relationship illustrate the construction of the table assembly;

FIGS. 2a and 2b are respectively partial left and right top plan views taken along the direction of line 2--2 in FIGS. 1a and 1b through the table assembly and when placed in a slightly overlapping relationship further illustrate the construction of the table assembly;

FIGS. 3a and 3b are respectively partial left and right views taken in section through the table assembly along the direction of line 3--3 in FIGS. 1a and 1b and when placed in a slightly overlapping relationship further illustrate the construction of the table assembly;

FIG. 4 is an enlarged view of a portion of the left side of the table assembly shown in FIG. 1a and illustrates an annular positioning mechanism in a disengaged condition so as to allow indexing rotation of an index table of the assembly;

FIG. 5 is an enlarged partial view illustrating a portion of the right side of the table assembly shown in FIG. 1b but with the annular positioning mechanism in an engaged condition to provide positioning of the table assembly;

FIG. 6 is a schematic plan view taken along the direction of line 6--6 in FIGS. 1a and 1b and illustrates a polygonal drive coupling upon rotatively driving of the table for indexing;

FIG. 7 is a schematic plan view similar to FIG. 6 but illustrating the coupling after indexing rotation and positioning of the table;

FIG. 8 is a partial view that illustrates a modified construction of the drive coupling;

FIG. 9 is a partial sectional view of the table assembly similar to FIG. 1b to illustrate a lift mechanism that removes weight of the table from stationary supports during the indexing;

FIG. 10 is a sectional view through the table assembly similar to FIG. 9 but taken at a slightly different location to illustrate a lubrication system that provides lubrication during the indexing;

FIG. 11 is an elevational view of lift members of the lift mechanism and is taken along the direction of line 11--11 in FIG. 9;

FIG. 12 is a top plan view taken along the direction of line 12--12 in FIG. 11 to further illustrate the construction of the lift member;

FIG. 13 is an end view taken along the direction of line 13--13 in FIG. 11 to further illustrate of the lift member; and

FIG. 14 is a sectional view taken along the direction of line 14-14 in FIG. 11 to further illustrate the construction of the lift member.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to FIGS. 1a and 1b, a rotary index table assembly constructed in accordance with the present invention is generally indicated by 10 and includes a base 12 and a rotary index table 14 having a central rotational axis A and an outer periphery 16 which has a round shape as best illustrated in FIGS. 2a and 2b. A rotary drive 18 of the table assembly is illustrated in FIGS. 1a and 3a and operates to rotate the index table 14 on the base 12 for indexing rotation about the rotational axis A. Stationary supports 20 are suitably mounted in a fixed relationship as is the base 12 and support the periphery 16 of the table to prevent movement thereof during machining of a workpiece supported on the table by an unshown holder.

As illustrated in FIGS. 1a and 1b as well as in FIGS. 4 and 5, the table assembly 10 includes an annular positioning mechanism 22 including a base mounted crown gear 24, a table mounted crown gear 26, and a movable crown gear 28. Each of these crown gears has an annular shape with vertically projecting teeth. More specifically, the base and table mounted crown gears 24 and 26 have teeth that project upwardly, while the movable crown gear 28 has teeth that project downwardly. During operation of the table assembly as is hereinafter more fully described, the movable crown gear 28 is moved upwardly as shown in FIG. 4 so that it is disengaged from the base mounted crown gear 24 and the table mounted crown gear 26 to permit the indexing rotation of the table 14. After the indexing, the movable crown gear 28 is moved downwardly into engagement with the base mounted crown gear 24 and table mounted crown gear 26 to locate the table with respect to the base. The teeth of the crown gears 24, 26 and 28 extend radially with respect to the rotational axis A and taper inwardly so that the engagement of the movable crown gear 28 with the table mounted crown gear 24 and with the base crown gear 26 provides centering of the table as well as rotational positioning of the table with respect to the rotational axis after each indexing rotation.

As illustrated in FIGS. 1a and 1b as well as in FIGS. 4 and 5, the table assembly 10 also includes an air bearing 30 that may be utilized as an auxiliary lift to the lift mechanism that is hereinafter described to support the table 14 on the base 12 during the indexing rotation and the positioning of the table by the annular positioning mechanism 22. This support of the table by the lift mechanism provides more accurate table positioning by removing weight of the table from the supports 20 located below the table periphery 16. It should be noted that the table positioning can be achieved by lifting that counteracts less than the entire weight of the table, but best results are achieved when the entire weight of the table is lifted from the supports 20. The air bearing 30 prevents any dust or other foreign matter from entering the table assembly 10 as the table 14 is lifted from the base 12 for the indexing rotation as well as between the rotary index cycles.

As illustrated by combined reference to FIGS. 1a and 3a, the rotary drive 18 includes a double enveloping worm gear set 32 that rotates the table 14 as is hereinafter more fully described. Rotary drive 18 also includes a polygonal drive coupling 34 which, as shown in FIGS. 6 and 7, has a plurality of drive lobes 36 that rotate the table 14. Provision of both the double enveloping worm gear set 32 and the polygonal drive coupling 34 provides a relatively compact unit that is nevertheless capable of transmitting relatively large torque loads. This results because of the fact that both the double enveloping worm gear set 32 and the polygonal drive coupling 34 have surface-to-surface contact in transmitting the driving force as compared to line contact involved with other types of straight worm gear sets and other rotary couplings.

As illustrated in FIG. 3a, the double enveloping worm gear set 32 includes a worm 38 having opposite ends 40 which are respectively supported by a pair of anti-friction bearing assemblies 42. Each bearing assembly 42 has an inner race 44 that supports the associated worm end 40, tapered bearing element 46 that roll around the inner race 44, and an outer race 48 that is supported on the base with the tapered bearing elements rollingly supported thereby so as to thus support the worm for rotation about an associated axis B. Between its ends 40, the worm 38 has an inwardly curved shape 50 that extends about the rotational axis A to provide the one enveloping function of the worm gear set. In addition, the worm gear set includes a worm gear 52 that is rotatably supported about the rotational axis A as is hereinafter more fully described to provide rotational driving of the table 14. This worm gear 52 as shown in FIGS. 1a and 4 has a curved shape 53 about the worm axis B so as to provide the other enveloping function of the worm gear set. A suitable schematically illustrated connection 54 shown in FIG. 3a provides rotational driving of the worm 38 by an unshown electric motor or other rotary prime mover such that the worm rotates the worm gear 52 to rotate the table during the indexing cycle as is hereinafter more fully described.

As best illustrated by combined reference to FIGS. 1a and 1b, the polygonal drive coupling 34 includes a coupling member 56 which is rotatively supported on the base 12 by lower and upper antifriction bearing assemblies 58 and 60, respectively. Each of these bearing assemblies includes an associated inner race 62 that is mounted by an associated bearing seat of the coupling member 56, tapered bearing elements 64 that roll about the inner race 62 around rotational axis A, and an outer race 66 that is mounted by the base 12 such that the coupling member is thus rotatably supported about rotational axis A. Worm gear 52 is secured to the coupling member 56 by a plurality of circumferentially spaced bolts 68, only one of which is illustrated in FIG. 1b. This securement is located adjacent the lower antifriction bearing assembly 58 in a spaced relationship from the upper antifriction bearing assembly 60. Above the upper antifriction bearing assembly 60, the coupling member 56 includes a drive portion 70 that is located within a downwardly extending driven portion 72 of the table 14. As illustrated in FIGS. 6 and 7, the drive portion 70 of the coupling member 56 includes the drive lobes 36 of the drive coupling and, as shown, there are four such drive lobes. The driven portion 72 of the table has a slightly larger size than the coupling member drive portion 70 as best shown in FIG. 7 so as to thus allow both radial and circumferential positioning of the table by the positioning member as was previously described and as will hereinafter be more fully described. Rotational driving of the coupling member 56 by the rotary drive previously described rotates the driving portion 70 a small angle C before there is any engagement of the drive lobes 36 with the driven portion 72. This free movement results from the fact that, as mentioned above, the driving portion 70 has a smaller size than the table driven portion 72. After such free movement, the drive lobes 36 of the driving portion 70 engage the table driven portion 72 with surface-to-surface contact as shown at areas 74 that are spaced at 90° intervals from each other about the rotational axis A. This distribution of the driving force allows a relatively large torque to be transmitted by a relatively compact coupling construction.

Cooperation of the double enveloping worm gear set 32 and the drive coupling 34 with the polygonal drive lobes 36 thus provides a relatively compact rotary drive that is nevertheless capable of transmitting relatively large torques during the table indexing while still permitting the table positioning in association with the positioning mechanism 22 and air bearing 30 previously described.

As illustrated in FIG. 8, it should be noted that the driven portion 72 with the lobe construction shown can be manufactured more easily when provided with reliefs 76 adjacent the lobes 36.

With combined reference to FIGS. 1a, 1b, 2a, 2b, 4 and 5, the annular positioning mechanism 22 that positions the table 14 includes a plurality of springs 77 that are spaced circumferentially around the rotational axis A and bias the movable crown gear 28 into engagement with the base mounted crown gear 24 and the table mounted crown gear 26. As best illustrated in FIGS. 4 and 5, the movable crown gear 28 includes an annular piston portion 78 that is slidably engaged in a sealed relationship with an upper annular seal 80 on the base 12. A lower annular seal 82 is slidably engaged in a sealed relationship with the movable crown gear 28 at a location below the piston portion 78 to thus cooperate the upper seal in providing an annular piston chamber 84. A hydraulic circuit 86 having an inlet 88 shown in FIGS. 1a and 4 and having a passage 90 that feeds the pressurized hydraulic fluid to the annular piston chamber 84 thereby moves the movable crown gear 28 against the bias of the springs 77. This movement of the movable crown gear 28 provides disengagement thereof with the base mounted crown gear 24 and the table mounted crown gear 26 to permit the indexing rotation of the table 14 under the impetus of the rotary drive previously described.

As best illustrated in FIG. 4, the air bearing 30 includes an annular bearing surface 92 which is part of the base 12 and faces upwardly. The table mounted crown gear 26 is slidably supported by the annular bearing surface 92 which has an annular recess 94 to which pressurized air is supplied to assist the lift mechanism which is hereinafter described in supporting the table on the base for the indexing rotation and for positioning as the movable crown gear 28 is engaged with the base mounted crown gear 24 and the table mounted crown gear 26. The pressurized air flows both outwardly and inwardly along bearing surface 92 as a film for supporting the table. The air is easily exhausted to the environment at the outer side of bearing surface 92 and is exhausted at the inner side of the bearing surface through passages 96 in the base 12 to the environment.

After the indexing and positioning, it is also desirable for the air bearing 30 to continue to supply pressurized air so that there is continual air flow that continues to prevent dust, machining coolant and any other foreign matter from entering the table assembly at the bearing surface 92. The air flow that continues between the indexing cycles also provides a continual cleaning action of the bearing surface 92. Satisfactory results have been achieved with the pressurized air being supplied between the rotary indexing cycles at a pressure of approximately five pounds per square inch to prevent foreign matter from entering the table assembly and at higher pressures to assist the lift mechanism in lifting the table 14 from the base 12. It should also be appreciated that while it is most preferable to utilize atmospheric air, it is also possible for the air bearing to use another gas such as, for example, nitrogen.

As best illustrated in FIG. 4, the base mounted crown gear 24 is secured to the base 12 by a plurality of circumferentially spaced bolts 98, only one of which is shown. This base mounted crown gear 24 also has a stop 100 that limits upward movement of the table mounted crown gear 26 to about twenty thousandths of an inch. More specifically, the stop 100 has an annular shape that projects radially above an annular stop 102 on the table mounted crown gear 26. Table 14 includes an annular flange 104 that projects downwardly and has the crown gear 26 mounted thereon and secured by a plurality of circumferentially spaced bolts 106, only one of which is shown. More specifically, the table mounted crown gear has a flange 108 that projects radially outward with the bolts 106 extending upwardly through associated holes in this flange for securement to the downwardly projecting table flange 104. Bolts 106 also extend through and mount an oil drip member 110 of an annular shape. This oil drip member 110 as shown in FIGS. 4 and 5 has an annular notch 111 that prevents machining coolant from wicking upwardly toward the outer extremity of the bearing surface 92. As illustrated in FIG. 1b, drip member 110 also has circumferentially spaced vertical holes 112, only one shown, receiving downwardly projecting guide pins 114 that extend downwardly from the table flange 104 through associated holes in the flange 108 of the table mounted crown gear 26 to thereby facilitate the assembly.

With reference to FIGS. 1a and 1b, the table 14 as described above includes the annular flange 104 on which the table mounted crown gear 26 is secured, and the base mounted crown gear 24 is mounted on the base 12 within the confines of the table mounted crown gear. Furthermore, the piston portion 78 of the movable crown gear 28 extends inwardly toward the rotational axis and is located inwardly from the base mounted crown gear 24. Furthermore, the springs 77 that bias the movable crown gear 28 are located outwardly from the piston portion 78 thereof in alignment with both the base mounted crown gear 24 and the table mounted crown gear 26. More specifically, the base 12 has an annular ring 116 that is secured by bolts 118 to the rest of the base and projects radially outward from the rotational axis A above the movable crown gear 28. Springs 77 are of the helical type and have upper ends received within downwardly opening holes 120 spaced circumferentially about the base ring 116. Lower ends of the springs 77 are received within upwardly opening holes 122 spaced circumferentially about the movable crown gear 28 to thus provide the downward bias of the movable crown gear into engagement with the base and table mounted crown gears 24 and 26.

As illustrated in FIG. 1a, the table assembly 10 also includes a sensor assembly 124 for detecting when the table 14 has rotated to each indexed position. More specifically, this sensor assembly 124 includes a stationary support member 126 mounted adjacent the table base 12 in a fixed position and having an upper end on which a sensor 128 such as a proximity sensor is mounted. The periphery 16 of the table 14 has sensor members 130 respectively positioned circumferentially thereabout at each rotational position to which the table 14 is to be indexed. Thus, positioning of the table 14 by the rotary drive previously described at each index position is sensed by the sensor assembly 124 to verify that the table assembly is ready for the next cycle of workpiece processing to commence.

As illustrated in FIG. 5, the table assembly 10 also includes a sensor assembly 132 for detecting whether the positioning mechanism 22 is in the crown gear engaged condition or disengaged condition. More specifically, this sensor assembly 132 includes a sensor member 134 that has an upper end secured to the movable crown gear 28 and that extends downwardly through a hole 136 in the base mounted crown gear 24 to a sensor 138 mounted on the base 12. Upward and downward movement of the sensor member 134 along with the movable crown gear 28 is thus sensed by the sensor 138.

With reference to FIG. 9 while taking into consideration the previous description of FIGS. 1a and 1b, the table assembly 10 also includes a lift mechanism 140 that removes weight of the table 14 from the stationary supports 20 by the impetus of the movable crown gear 28 upon moving out of engagement with the base mounted crown gear 24 and the table mounted crown gear 26. This lifting facilitates accurate table positioning when the movable crown gear 28 is subsequently again moved into engagement with the base mounted crown gear 24 and the table mounted crown gear 26 after the indexing rotation of the table 14. As previously discussed, the engagement and disengagement of the movable crown gear 28 with the base mounted crown gear 24 and the table mounted crown gear 26 is controlled by the cooperation of the springs 77 and the hydraulic fluid supplied through passage 84 (FIG. 1b) to the piston portion 78 that extends inwardly from the main portion of the movable crown gear.

With combined reference to FIGS. 2a and 2b, 9 and 11-11, the lift mechanism 140 includes lift members 142 that are spaced circumferentially around the table 14 and that are moved upwardly by the movable crown gear 28 upon disengagement thereof from the base mounted crown gear 24 and the table mounted crown gear 26. This lifting of the table 14 removes weight of the table from the stationary supports 20 at the table periphery 16. As illustrated in FIG. 9. The base 12 as previously described has an annular ring 116 that, as illustrated by continuing reference to FIG. 9, has vertical openings 144 that respectively receive the lift members 142. These lift members 142 extend vertically between the movable crown gear 28 and the table 14 after disengagement of the movable crown gear from, the base and table mounted crown gears 24 and 26 as illustrated by phantom line representation. Thus, the hydraulic fluid acting on the piston portion 78 of the movable crown gear 28 against the bias of the spring 77 (FIGS. 1a and 1b) provides the upward movement of the movable crown gear and the impetus for the lifting of the table 14 via the lift members 142 extending through the openings 144 of the base ring 116.

As illustrated in FIG. 11, each lift member 142 has a lower surface 146 for engaging the movable crown gear 28 and also has an upper surface 148 for engaging the table 14. With combined reference to FIGS. 11-14, each lift member 142 includes at least one hardened lift button 150 providing its lower surface 146. The lift members 142 each have a horizontally elongated shape having opposite ends 152 that are illustrated as being chamfered as viewed in FIG. 2 so as to have a somewhat pointed shape. A pair of the lift buttons 150 are respectively mounted by the opposite ends 152 of each lift member and cooperatively provide the lower surface 146 that engages the movable crown gear 28 during the lifting. Furthermore, each lift member 142 preferably includes a third lift button 150 mounted between the pair of lift buttons at the opposite ends 152 thereof and cooperating therewith to provide the lower surface 146 for engaging the movable crown gear 28. Each lift button 150 has an upwardly extending shank 154 (FIG. 11) received within an associated hole in the lift member and secured by a threaded fastener 156 (FIG. 12).

As illustrated by combined reference to FIGS. 1a, 2b and 9, the table also has a lower glide ring 158 that has an annular shape extending about the central axis of the table assembly. This lower glide ring 158 is engaged by the upper surfaces 148 of the lift members under the impetus of the upward movement of the movable crown gear 28 during the lifting. Lower glide ring 158 is made of a hardened metal to prevent wear.

With combined reference to FIGS. 2a, 2b and 10, the table assembly also includes a lubrication system 160 including wicks 162 mounted by the annular ring 116 of the base between the vertical openings 144 (FIG. 9) that receive the lift members 142. The lubrication system 160 includes lubricating passages 164 for feeding a lubrication fluid to the wicks 162 to provide lubrication between the upper surfaces 148 of the lift members 142 and the lower glide ring 158 of the table 14 as shown in FIG. 9.

With reference to FIGS. 12 and 14, each lift member 142 has at least one elastomeric locator 166 for restraining movement of the lift member within the associated vertical opening 144 of the annular ring 116 of the base 12. More specifically, the horizontally elongated shape of the lift member 142 has a pair of the elastomeric locators 166 in the preferred construction. Each horizontally elongated lift member 142 has a pair of horizontal holes 168 extending transverse to its elongated direction. A pair of the elastomeric locators 166 respectively extend through the pair of horizontal holes 168 and, as shown in FIG. 14, have opposite ends 170 that engage the annular ring 116 of base 12 to restrain the lift member movement.

While the best mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims. 

What is claimed is:
 1. A rotary index table assembly comprising : a base; a rotary index table having a central rotational axis and an outer periphery; a rotary drive that rotates the index table on the base for indexing rotation about the rotational axis; stationary supports that support the periphery of the table to prevent movement thereof during machining of a workpiece supported by the table; an annular positioning mechanism including a base mounted crown gear, a table mounted crown gear and a movable crown gear that is moved to disengage from the base mounted crown gear and the table mounted crown gear to permit the indexing rotation of the table and that is thereafter moved into engagement with the base mounted crown gear and the table mounted crown gear to locate the table with respect to the base after each indexing rotation; and a lift mechanism that removes weight of the table from the stationary supports by the impetus of the movable crown gear upon moving out of engagement with the base mounted crown gear and the table mounted crown gear to facilitate accurate table positioning when the movable crown gear is subsequently again moved into engagement with the base mounted crown gear and the table mounted crown gear after the indexing rotation of the table.
 2. A rotary index table assembly as in claim 1 wherein the lift mechanism includes lift members that are moved upwardly by the movable crown gear upon disengagement thereof from the base mounted crown gear and the table mounted crown gear to remove weight of the table from the stationary supports.
 3. A rotary index table assembly as in claim 2 wherein the base includes an annular ring having vertical openings that receive the lift members, and the lift members extending vertically between the movable crown gear and the table after disengagement of the movable crown gear from the base and table mounted crown gears.
 4. A rotary index table assembly as in claim 3 wherein each lift member has a lower surface for engaging the movable crown gear and an upper surface for engaging the table.
 5. A rotary index table assembly as in claim 4 wherein each lift member includes at least one lift button providing the lower surface thereof for engaging the movable crown gear.
 6. A rotary index table assembly as in claim 4 wherein each lift member has a horizontally elongated shape having opposite ends, and a pair of lift buttons respectively mounted by the opposite ends of each lift member and cooperatively providing the lower surface thereof for engaging the movable crown gear.
 7. A rotary index table assembly as in claim 6 wherein each lift member also includes a third lift button mounted between the pair of lift buttons at the opposite ends thereof and cooperating therewith to provide the lower surface thereof for engaging the movable crown gear.
 8. A rotary index table assembly as in claim 4 wherein the table has a lower glide ring of an annular shape that is engaged by the upper surfaces of the lift members.
 9. A rotary index table assembly as in claim 8 further including a lubrication system for providing lubrication between the glide ring and the lift members.
 10. A rotary index table assembly as in claim 9 wherein the lubrication system includes lubrication wicks mounted by the annular ring of the base between the vertical openings that receive the lift members, and the lubrication system also including lubrication passages for feeding a lubrication fluid to the wicks to provide lubrication between the upper surfaces of the lift members and the lower glide ring of the table.
 11. A rotary index table assembly as in claim 4 wherein each lift member includes at least one elastomeric locator for restraining movement thereof within the associated vertical opening of the annular ring of the base.
 12. A rotary index table assembly as in claim 11 wherein each lift member has a horizontally elongated shape and a pair of the elastomeric locators, each horizontally elongated lift member having a pair of horizontal holes extending therethrough, and the pair of elastomeric locators respectively extending through the pair of horizontal holes and having opposite ends that engage the annular ring of the base within the associated vertical opening thereof to restrain the lift member movement.
 13. A rotary index table assembly as in claim 1, 2, 3, 4 or 9 wherein the annular positioning mechanism includes a plurality of springs that bias the movable crown gear into engagement with the base mounted crown gear and with the table mounted crown gear, the movable crown gear including an annular piston portion, and a hydraulic circuit that selectively provides pressurized hydraulic fluid to the piston portion of the movable crown gear to thereby provide movement thereof against the bias of the springs out of engagement with the base mounted crown gear and the table mounted crown gear to permit the indexing rotation under the impetus of the rotary drive.
 14. A rotary index table assembly as in claim 13 wherein the piston portion of the movable crown gear extends inwardly toward the rotational axis.
 15. A rotary index table assembly as in claim 14 wherein the piston portion of the movable crown gear is located inwardly from the base mounted crown gear, and the springs that bias the movable crown gear being located outwardly from the piston portion thereof in alignment with both the base mounted crown gear and the table mounted crown gear.
 16. A rotary index table assembly comprising: a base; a rotary index table having a central rotational axis and an outer periphery; a rotary drive that rotates the index table on the base for indexing rotation about the rotational axis; stationary supports that support the periphery of the table to prevent movement thereof during machining of a workpiece supported by the table; an annular positioning mechanism including a base mounted crown gear, a table mounted crown gear and a movable crown gear that is moved to disengage from the base mounted crown gear and the table mounted crown gear to permit the indexing rotation of the table and that is thereafter moved into engagement with the base mounted crown gear and the table mounted crown gear to locate the table with respect to the base after each indexing rotation; and a lift mechanism including lift members that extend between the table and movable crown gear to remove weight of the table from the stationary supports by the impetus of the movable crown gear upon moving out of engagement with the base mounted crown gear and the table mounted crown gear to facilitate accurate table positioning when the movable crown gear is subsequently again moved into engagement with the base mounted crown gear and the table mounted crown gear after the indexing rotation of the table.
 17. A rotary index table assembly comprising: a base; a rotary index table having a central rotational axis and an outer periphery; a rotary drive that rotates the index table on the base for indexing rotation about the rotational axis; stationary supports that support the periphery of the table to prevent movement thereof during machining of a workpiece supported by the table; an annular positioning mechanism including a base mounted crown gear, a table mounted crown gear, a movable crown gear that has a piston portion and is moved to disengage from the base mounted crown gear and the table mounted crown gear to permit the indexing rotation of the table, and a plurality of springs that bias the movable crown gear into engagement with the base mounted crown gear and the table mounted crown gear to locate the table with respect to the base after each indexing rotation; and a lift mechanism including a hydraulic circuit that selectively provides pressurized hydraulic fluid to the piston portion of the movable crown gear to thereby provide movement thereof against the bias of the springs out of engagement with the base mounted crown gear and the table mounted crown gear to permit the indexing rotation under the impetus of the rotary drive, and the lift mechanism including lift members that extend between the table and movable crown gear to remove weight of the table from the stationary supports by the impetus of the movable crown gear upon moving out of engagement with the base mounted crown gear and the table mounted crown gear to facilitate accurate table positioning when the movable crown gear is subsequently again moved into engagement with the base mounted crown gear and the table mounted crown gear after the indexing rotation of the table.
 18. A rotary index table assembly comprising: a base having an annular ring including circumferentially spaced vertical openings extending therethrough; a rotary index table having a central rotational axis and an outer periphery; the table having a lower glide ring; a rotary drive that rotates the index table on the base for indexing rotation about the rotational axis; stationary supports that support the periphery of the table to prevent movement thereof during machining of a workpiece supported by the table; an annular positioning mechanism including a base mounted crown gear, a table mounted crown gear, a movable crown gear that has a piston portion and is moved to disengage from the base mounted crown gear and the table mounted crown gear to permit the indexing rotation of the table, and a plurality of springs that bias the movable crown gear into engagement with the base mounted crown gear and the table mounted crown gear to locate the table with respect to the base after each indexing rotation; a lift mechanism including a hydraulic circuit that selectively provides pressurized hydraulic fluid to the piston portion of the movable crown gear to thereby provide movement thereof against the bias of the springs out of engagement with the base mounted crown gear and the table mounted crown gear to permit the indexing rotation under the impetus of the rotary drive, the lift mechanism including lift members that are respectively received by the vertical openings of the annular ring of the base, the lift members extending between the lower glide ring of the table and the movable crown gear to remove weight of the table from the stationary supports by the impetus of the movable crown gear upon moving out of engagement with the base mounted crown gear and the table mounted crown gear to facilitate accurate table positioning when the movable crown gear is subsequently again moved into engagement with the base mounted crown gear and the table mounted crown gear after the indexing rotation of the table; and a lubrication system for providing lubrication between the lower glide ring of the table and the lift members. 